Bug fix: It was possible to start synchronization in new window despite incompatible "Selected files only" option selected by Shift-clicking the OK button

https://winscp.net/tracker/1870

Source commit: 98a25451159220c7a186dd17d420b9b3d2fb7dd1

source/forms/FullSynchronize.cpp

@@ -474,8 +474,8 @@ void __fastcall TFullSynchronizeDialog::OkButtonClick(TObject *)
     else
     {
       Beep();
+      ModalResult = mrNone;
     }
-    Abort();
   }
 }
 //---------------------------------------------------------------------------